Methods of and devices for continuously packaging articles in thermoshrinkable plastics film

ABSTRACT

A method and device for continuously packaging articles in thermoshrinkable plastics film. Such a device comprises an endless chain conveyor driving equidistant trays articulated so as always to remain horizontal while following a roller path CR. This conveyor, between a feed station FC for the collections of articles to be wrapped and a discharge station for the collections closed and wrapped in their shrunk wrapping, comprises a device for loosely wrapping each collection, a thermoshrinkage zone, an upper finishing zone and a descending cooling zone at the exit from which the collections may be handled without risk, as soon as they arrive at the discharge station. This device comprises in addition a continuous reel handler for an upper film and a similar reel handler for a lower film, these films being intended for making up the wrappings of the collections of articles. The invention is applicable to the techniques of providing an outer wrapping to articles, of thermoshrinkable plastics film.

[451 Mar. 11, 1975 1 1 METHODS OF AND DEVICES FOR CONTINUOUSLY PACKAGINGARTICLES IN TI-IERMOSHRINKABLE PLASTICS FILM [75] Inventor: Pierre PaulEdouard, Essonne,

France [73] Assignee: Lara SA.

[22] Filed: Aug. 31, 1973 [21] App]. No.: 393,481

[30] Foreign Application Priority Data Sept. 4, 1972 France 72.31291Sept. 25, 1972 France 72.33890 [52] US. Cl 53/30, 34/216, 34/225,53/182, 53/184, 219/388 [51] Int. Cl B651) 53/06, B65b l1/5O [58] Fieldof Search 53/30 S, 18 4 S, 182, 184 S; 34/20l203, 209, 210, 211, 212,215, 216, 217, 218, 225; 219/388 3,727,324 4/1973 Melgaard... 34/2163,736,723 6/1973 Lattke 53/184 S X 3,766,708 10/1973 Kubo et a1. 53/184S X Primary ExaminerRobert L. Sprui11 Attorney, Agent, or Firm-Bacon &Thomas [57] ABSTRACT A method and device for continuously packagingarticles in thermoshrinkable plastics film. Such a device comprises anendless chain conveyor driving equidistant trays articulated so asalways to remain horizontal while following a roller path CR. Thisconveyor, be-

tween a feed station PC for the collections of articles to be wrappedand a discharge station for the collections closed and wrapped in theirshrunk wrapping. comprises a device for loosely wrapping eachcollection, a thermoshrinkage zone, an upper finishing zone and adescending cooling zone at the exit from which the collections may behandled without risk, as soon as they arrive at the discharge station.This device comprises in addition a continuous reel handler for an upperfilm and a similar reel handler for a lower film, these films beingintended for making up the wrappings of the collections of articles. Theinvention is applicable to the techniques of providing an outer wrappingto articles, of thermoshrinkable plastics film.

20 Claims, 12 Drawing Figures PATENTED'HARI 1197s SHEET 3 [IF 8 PATENTEBMARI 1 I975 SHEET b UF 8 PATENTEDNARI 11916 3.869 844 snmsura METHODS OFAND DEVICES FOR CONTINUOUSLY PACKAGING ARTICLES IN THERMOSHRINKABLEPLASTICS FILM The present invention relates to methods and devices forcontinuously packaging articles in thermoshrinkable plastics film and,more especially, it deals with a method for continuously packagingarticles or collections (bulkings) of articles in a wrapping ofthermoshrinkable plastics film, such as PVC or polyethylene film; italso relates to a device for applying this method, in the form of asingle machine fitted with a tray conveyor, which is so constructed asto move continuously; upon each tray of this conveyor there are carriedout, without interruption, first the receiving of an article orcollection of articles, then the placing and sealing of a loose wrappingof film around the article or collection, the wrapping extendinglaterally on either side of it, then the thermoshrink'age of thiswrapping, followed by cooling sufficient to enable the package thusproduced to be removed and handled without risk of deterioration, assoon as it leaves the conveyor; the conveyor meanwhile continues itsreturn journey, empty, towards its entry point, where it takes over newcollections of articles to be wrapped.

In the prior art of packaging using thermoshrinkable film, numeroustypes of device are known which are capable of effecting one of theaforementioned operations individually; these devices may be combinedtogether to act in conjunction carrying out, consecutively but notcontinuously, these various operations for the production of packages ofarticles in shrunk wrappings. This lack of continuity in the successionof operations is due, in fact, to the excessively large dimensions,especially longitudinally, of these devices, which does not allow themto be placed in line in view of the restricted space available in themajority of cases, both for perblown, followed by a long cooling zone,that is to say a zone where cold air or any other refrigerated fluid isprojected upon the shrunk packages, these packages being consideredsufficiently rigid to be handled when they leave this cooling zone.These known devices possess in general a disadvantage which isconsidered to be a serious one, in that they are too bulky, especiallyin their length; other disadvantages result from the fact that they donot always enable the thermoshrinkage operation to be carried out in asuitable manner, because of the unconsidered losses of hot air, nor dothey enable the cooling operation to be satisfactorily effected since,in general, in spite of their very great length along the ground, thecooling zone of these devices is too short, with the result that thepackages, still warm, cannot be handled immediately upon leaving thiscooling zone, without risk of defects being produced.

It is moreover relatively uncommon, because of the different designs ofthese numerous devices, for it to be possible to combine them for thepurpose of effective overall functioning; for this reason, anintermediate handling of the articles or collections of articles betweeneach pair of operations is often required, thus still further increasingthe number of disadvantages which these devices of the prior art arerecognized to possess. Moreover, in these known devices, the lower filmwhich is to constitute the bottom and the sides, transversely to theconveyor, of the thermoshrinkable wrapping, is first placed upon saidconveyor before each collection of articles is placed upon it, followedby the placing of an upper film over the articles to constitute theupper part of the wrapping; this upper film will later be joined to thetransverse sides. This known method for placing the wrapping possessescertain disadvantages in that, in order to carry it out, eachtransporting element of the conveyor intended to receive a collection ofarticles must be in the form of a trough adapted substantially to thewidth and height of the collection, in order that the lower film shallfollow the shape of its underside and of its sides, while it is waitingto be joined to the upper film which will follow the shape of the top ofthe collection of articles.

It is, therefore, one of the principal objectives of the presentinvention to provide a single device in the form of a machine which isshort by comparison with the installations of known type constituted ofa number of devices, and which is capable of carrying out a continuousprocess for the packaging of articles or collections of articles inwrapping of shrinkable film; this process also constitutes one of theobjectives of the invention and overcomes the greater part of thedisadvantages mentioned above.

Another objective is to provide such a machine, which operatescontinuously and does not require any handling of the collections ofarticles from the stage where they are taken over by the machine to thatwhere they are removed in the condition of firmly closed packages, norany surveillance at any time, but which requires only the replacing ofthe reels of empty film by other, full reels, so that the feed ofthermoshrinkable film may be ensured without either stopping or cutting.

Another objective is to provide such a machine, so constructed as topossess an advantageous characteristic in the operation of placing loosewrapping material around each collection of articles, in that it takesover the collection while it is already resting upon the lower film,which in turn rests upon a fixed feeding fork.

Yet a further objective of the invention is to provide such a machine,designed in such a way that the portion of it corresponding to thethermoshrinkage and cooling station for the wrappings is of very shortlength along the ground, while still providing sufficient developedlength to enable these operations to be effectively carried out and topermit the handling, without risk of deformation, of the closed andwrapped collections as soon as they leave this station; this result isachieved utilizing the ascending property of hot air in the shrinkagezone and, conversely, the property of cold air of falling in the coolingzone, the shrinking zone being a portion having a steep ascending slope,close to the vertical, while the cooling zone is, by contrast, a portionhaving a steeply descending slope, of sufficient length to ensureeffective cooling of the shrunk collections. thus enabling them to behandled as soon as they leave that zone. In addition, this machineutilizes a chain conveyor having articulated trays and movingcontinuously, enabling the unwrapped articles or collections of articlesto be received by the machine at the feed station, without interruptionone after another, enabling them then to be passed continuously to thenext station where they are fitted with their loose wrapping ofthermoshrinkable plastics film, then to be conveyed, provided with theirwrapping, first to the shrinkage zone and, after that, to the coolingzone, this being done without changing, anywhere along the path, theposition in which they were originally fed and in which they will bedischarged, tightly wrapped and ready to be handled, at the outlet fromthe cooling zone.

According to the invention, the method of continuously packagingarticles and, notably, collections of articles in a wrapping ofthermoshrinkable plastics film, based upon the use of a continuouslymoving tray conveyor, comprises the following operations:

1. The reception, by each tray, of an article or collection of articlesplaced thereon, resting upon a lower film, at the feed station;

2. The covering of the collection with an upper film, a free end ofwhich is joined to that of the lower film at the front of the collectionof articles;

3. Joining of the upper film to the lower film at the rear of saidcollection of articles and median cutting of the film providing at thisstage, respectively, the closure edge for the loose wrapping of thiscollection and the starting joint for the wrapping of the nextcollection;

4. The transporting of each collection, loosely wrapped, into apreheating zone, followed by an ascending thermoshrinkage zone, theninto a thermoshrinkage finishing zone and, finally, into a descendingcooling zone, terminating in a discharging station, at which thecollections, tightly wrapped and closed, may immediately be handled.

' It should be noted that the last operation, constituting thethermoshrinkage and cooling operation for the film wrappings is, inaccordance with the invention, carried out in a station constituted of apath substantially in the form of an open, inverted U, this path beingfollowed by the conveyor with its articulated trays for transporting thearticles or collections of articles, and one of the arms of this pathbeing sleeved in a hot air tunnel constituting an ascendingthermoshrinkage zone, while the other arm is open to the surrounding airbut just beneath a cooling assembly which subjects it to a draught ofcold air; this second arm constitutes a descending cooling zone, at theexit from which the col lections are sufficiently rigid to be handled.

More specifically and in accordance with the invention, this method isbased upon the use of an endless, straight-line conveyor, havingarticulated trays, spaced apart from one another and so designed as toremain horizontal along the totality of the path between the feedstation and the discharge station; the successive operations which themethod comprises are carried out uninterruptedly upon these trays, theseoperations being the following:

1. The reception, by each tray, of a collection of articles placed upona lower film resting upon a fixed feeding fork and raised up behind thecollection to provide a slack forming loop between that collection andthe following collection;

2. The covering and enveloping of the upper part of the collection ofarticles with an upper film a free end of which is joined to that of thelower film at the leading end of this collection;

3. The joining together and cutting, by heat sealing and cutting, of theupper film and the loop of slack of lower film behind the collection, soas to close its wrapping in the loose state and to separateit from thestarting edge of the wrapping of the following collection;

4. The transporting of the loosely wrapped collection into athermoshrinkage preheating zone, then into an ascending thermoshrinkagezone, then subsequently into a horizontal thermoshrinkage finishing zoneand, finally, into a descending cooling zone, at the exit from whicheach collection with its wrapping of film, now tightly closed, may bedischarged and may be immediately handled.

Still more specifically, and according to the invention, it should benoted that, in this method, with regard to operations (1) to (3), thelower and upper films are continuously fed without cutting and are of awidth greater than the dimensions of the collection as measuredperpendicularly to the longitudinalaxis of the conveyor, so that theyproject laterally, with respect to this axis, from these collections ofarticles. Moreover, during the operation of loading on its tray eachcollection, the loop of slack in the lower film is made while onecollection starts to be moved forward by a tray of the conveyor andwhile the front edge of the succeeding collection arrives at the rear ofthe fixed feeding fork, these two collections being separated by thesame distance as is maintained between them throughout the whole oftheir passage through the operational path of the conveyor, so that thefront side of the loop is jammed between the rear edge of the collectionon a tray and the rear of the same tray, and that the rear side of theloop is jammed between the front edge of the succeeding collection andthe rear edge of the feeding fork. In addition, each collection is movedforward over the feeding fork at the same speed as the advance speed ofthe conveyor, thus entraining the lower film jammed beneath it.Moreover, the height of each convex loop of slack in the lower filmbetween two collections is determined in such a way that the developmentof this loop is always less than the height of each collection so that,during the jointing operation, the joint line at the start of wrappingin front of this collection and also the joint line at the closure ofthis wrapping behind this collection are situated, respectively, in aregion of the front and rear faces of the collection, and not above Thedevice for applying thismethod is, according to the invention,constituted of:

a. A tray conveyor, moving continuously along a straight-line rollerpath passing from a fixed feeding fork for the collections to a fixed,similar, discharging fork, via a station for receiving and looselywrapping the collections, a preheating and thermoshrinkage station withan ascending path, a thermoshrinkage finishing station with a horizontalpath, and a station having a descending path for cooling the shrunkwrappings, this station leading into the discharge fork, the conveyorthen continuing its return path empty towards the feeding fork; y

b. An oscillating device, having heat sealing and cutting jaws, situatedin front of the feed fork, designed to join together and to cut thelower and upper films for forming a loose wrapping around eachcollection;

c. A device for forming a slack loop of lower film between twoconsecutivecollections;

d. A film reel handler supplying the upper film continuously and asimilar reel handler supplying the lower film continuously.

More specifically, this device for practicing the method according tothe invention is constituted of:

a. An endless conveyor entraining equally spaced trays and movingcontinuously, at uniform speed, following a straight-line roller pathcomprising, from a fixed feed fork for the collections to a similarfixed discharging fork for these collections when they have each beenfirmly closed and wrapped in a wrapping of shrunk plastics film, a firsthorizontal portion where the operations of receiving and looselywrapping the collections are carried out, an ascending portion having aslope close to the vertical where the preheating and thermoshrinkageoperations are carried out, a second horizontal portion where thethermoshrinkage finishing operation is carried out, and a descendingportion where the cooling is carried out, and which leads into a thirdhorizontal portion, in the same plane as the first and co-operating withthe fixed discharging fork, this roller path then continuing, in a planebelow the first and third horizontal portions but parallel to theseplanes, into a return portion connecting the discharging station to thefeed station;

b. A device with heat sealing and cutting jaws, mounted in the firsthorizontal portion, so as to enable jointing and cutting to be effectedacross the width of the upper and lower films for forming a loosewrapping and able to oscillate longitudinally relative to the conveyorin the forward and reverse direction through an angle encompassing thedistance between the axes of two consecutive gaps in front of and behinda collection of articles, and capable of separating its wrapping fromthe start of the wrapping of the following collection;

c. A device for forming a loop of slack in the lower film between twoconsecutive collections, situated behind the fixed feed fork in theextension of the roller path and constructed in the form of a balancearm, the free end of which can move upwards and downwards in order toraise the lower film both ahead and behind along a path exceeding thegap between two collections of articles;

, d. A film reel handler supplying the upper film continuously andsituated substantially vertically above the heat sealing and cuttingdevice above the first horizontal portion of the roller path, and asimilar reel handler, supplying the lower film continuously, situatedbehind and below the plane of the fixed feed fork, preferably laterallyto the rear extension of that feed fork, this extension being occupiedby a second conveyor for as- 'sembling the collections, comprising atthe front and close to the fork, a feed loader designed to push each ofthe collections onto the fork before they are placed on a tray of thefirst conveyor, at the same speed as that tal position in the ascendingand descending portions;

each tray comprises, in addition, rearrollers so positioned as to runalong the horizontal portions of the roller path and to keep the tray ina horizontal position along these portions of the path.

lt should be noted, in addition, that each tray of the conveyor isconstituted of ribs for supporting the collection resting upon it, theseribs extending parallel to the conveyor axis and parallel to oneanother, separated from one another by a gap larger than the width ofeach arm of each of the fixed forks and slightly higher than the heightof these forks, so that their upper plane is slightly above that of afork when they are brought by their respective tray to the horizontallevel of the feed and discharge stations so that, at the feed fork, theyraise and entrain the lower film with a collection upon it and, at thedischarge fork, they lower and deposit the collection with its shrunkwrapping upon that fork, without ever completely passing beyond the armsof these forks.

In addition, the jaw device for heat sealing and cutting is constitutedof a balance arm supporting reciprocating upper and lower jaws havingtheir heat sealing and cutting blades respectively facing each other,these jaws being so constructed that, when their balance arm is inclinedin the direction opposite to the direction of movement of the conveyor,they grip between them the upper and lower films between two successivecollections of articles, seal them and cut them apart during theoscillation of the balance arm in the direction of motion of theconveyor while the balance arm is substantially in a position close toits vertical median position, they open and move apart from each otherwhile the balance arm continues its oscillation in this same direction,until the lower jaw is in a lower position close to the axis of pivot ofthe balance arm and the upper jaw is at a position above the collectionsof articles, this upper jaw then lowering the upper film onto thecollection to be wrapped while the balance arm makes its returnoscillation to come back to its initial position; at this instant thelower jaw bears up underneath the loop of slack lower film and the upperjaw bears down on the upper film until it presses it onto the upper partof this loop; the operation of gripping the films then takes place andthe succeeding operations listed above are again carried out.

In addition, each of the reel handlers for the upper and lower films isconstituted of a roller cradle designed to support a reel of film whichis being used and a reserve reel, of a jaw device for heat sealingcutting comprising a central reversible jaw carrying the free end of thereserve film and two fixed jaws situated on either side of thisreversible jaw, outside but close to the path of the film in use and thepath which will be followed by the reserve film when it is being used,and (is constituted of) a film tensioning assembly for tensioning thefilm in use, directing this film via a roller direction changingassembly towards the corresponding film feeder of the packaging device,the construction of this reel handler being such that, when the film inuse comes to an end, the reversible jaw, assisted by the correspondingfixed jaw, joins the free end of the reserve film to this tail end ofthe used film, the tensioning device releasing film during thisoperation, so that there is no cessation of feed of film by the filmfeeder.

In addition, in this device according to the invention, in ordereffectively to carry out the fourth operation of the method, theascending portion in which the preheating and thermoshrinkage operationis carried out, and also the second horizontal portion of the rollerpath in which the thermoshrinkage finishing operation is carried out,are situated in a tunnel forming a sleeve along the roller path, andcomprising in its lower part an air ventilation assembly opening intothe curved .out is situated so as to be exposed to the surrounding airbut has immediately above it a cooling assembly constituted of aventilation assembly so constructed as to direct jets of cold air ontoeach of the shrinkwrapped collections of articles, in order to give themthe best environment to accelerate their cooling as soon as they leavethe top exit of the tunnel.

More specificially and according to the invention, these portionsconstitute, correctly speaking, the shrinkage device which comprises:

a. A roller path followed by a chain conveyor with articulated trays forsupporting collections of articles and having its entry and exit endshorizontally connected from the entry to the exit by an ascendingportion of very steep slope, an upper horizontal portion and adescending portion of lesser slope than that of the ascending portion;

b. A tunnel surrounding the entry end, the ascending portion and theupper portion of the roller path being of of dimensions sufficient topermit the free passage through it of the chain conveyor with its trayscarrying their loads, hot air being cycled through this tunnel; c. Acooling assembly above the descending portion and the exit end oftheroller path which are open to the surrounding air, this cooling assemblybeing so constructed as to feed cold air onto the collections ofarticles which have been subjected to thermoshrinkage, from the timewhen they leave the upper part of the tunnel.

In this shrinkage device, the two lateral chains constituting the chainconveyor are guided around return pinions to have a path sensibly closeto that of the roller path and they support, transversely between them,the trays articulated at their front part by means of cranks and guiderollers attached to each of them, these cranks being designed in such away that, with their rollers running along the roller path, theymaintain the trays in a horizontal position at all times in theascending and descending portions, each tray comprising, in addition,rear rollers so positioned as to run along the horizontal portions ofthe roller path and to maintain the tray in a horizontal position alongthese portions of the path.

The tunnel constituting the ascending thermoshrinkage zone comprisesthree consecutive heating zones, a preheating zone corresponding to thehorizontal inlet portion and to the curved commencement of the ascendingportion of the roller path, a progressive thermoshrinkage zone proper,corresponding to the ascending portion and to the curved commencement ofthe upper horizontal portion of this roller path, and a thermoshrinkagefinishing zone corresponding to said upper portion. This tunnelcomprises, at its lower part, an air ventilation assembly opening intothe curved commencement of the ascending portion close to the preheatingzone, in its ascending portion lateral groups of heating resistorsdistributed in the progressive ther- '8 moshrinkage zone and, in itsupper part, an air ventilation assembly opening into the finishing zoneand, within this zone, lateral groups of resistance heaters. Theventilation assembly of the lower part is constituted of at least oneblower of the suction and delivery type, arranged to direct air upwardsover the groupsof resistance heaters in order to surround the ascendingcollections of articles with progressively hotter air as they ascend andto draw this hot air out again atthe ceiling of the ascending portion bymeans of a recycling duct running beneath that ceiling and descending tothe blower along the internal walls of this acending portion, the partof this duct beneath the ceiling being provided with numerous intakeholes. The ventilation assembly for the upper portion is likewiseconstituted of at least one blower of the suction and delivery type,arranged to direct air upwards over the groups of resistance heaters inorder to provide hot air around the collections of articles advancingthrough the finishing zone towards the exit from the tunnel and toremove this hot air from the ceiling of this zone by means of arecycling duct running beneath the ceiling of the upper part of thetunnel and descending to the blower along the internal walls of thisupper part, the portion of this duct beneath the ceiling being providedwith numerous intake holes.

It should be noted also that the resistance heaters, in the form offinned resistors, are arranged in tiers all along the lateral internalwalls of the tunnel, both in its ascending portion and in its upperportion and are placed in front of the descending ducts for recycled hotair, towards the median plane of the tunnel, in order to ensure goodheat distribution.

In addition, in a still more specific'form of embodiment of this tunnel,each ventilation assembly delivers air into blowing ducts incorporatingthe heating resistors; these ducts, in the ascending portion of thetunnel, being placed in front of the recycling ducts towards the medianplane of the tunnel and being perforated on the side towards this planeto constitute a hot air blowing chamber having perforated lateral andbottom walls, the ceiling of which is traversed by the perforated partof the recycling duct and, in the upper part of the tunnel, being placedin the same manner but to constitute a hot air blowing chambercompletely surrounding the finishing zone and having lateral, upper andlower perforated walls, the perforated part of the recycling duct beingplaced beneath the ceiling of this upper part of the tunnel, in front ofthe chamber, close to the exit from the tunnel. It should be noted inaddition, that in order to limit the losses of hot air from this tunnel,the tunnel is provided with a lock, at its entry and at its exit, in theform of slotted, hanging curtains, to permit the passage of the traysand their collections of articles.

The cooling assembly. above the descending portion is constituted of aventilation assembly constructed to direct jets of cold air onto each ofthe shrink-wrapped collections of articles in order to give them thebest possible environment to accelerate their cooling.

Other characteristics and objectives of the present invention willbecome apparent from reading the description below, prepared in relationto the attached drawings, in which:

HO. 1 is a diagram illustrating how FIGS. 1A and 18 should be joinedtogether to provide a diagrammatic overall view of the packaging devicefor packaging collections of articles in thermoshrinkable plastics filmwrapping, forming the subject of the present invention,

FIG. 2 is a diagrammatic view of the feed station for the collections ofarticles, before they are wrapped,

FIG. 3 is a diagrammatic view of the discharge station for the closedand wrapped collections of articles after the operation ofthermoshrinkage and cooling of the thermoshrunk wrappings,

FIGS. 4, 5, 6 and 7 are diagrammatic representations of the successivestages of the operation of loosely wrapping the collections of articles,before the thermoshrinkage operation,

FIG. 8 is a section, along AA in FIG. 1B, of the ascending portion ofthe tunnel constituting the progressive thermoshrinkage zone, the rollerpath and the chains passing through this portion having been omitted forthe sake of clarity,

FIG. 9 is a section, along BB of FIG. 1B, of the upper part of thetunnel constituting the finishing zone; here again, as in FIG. 8, theroller path and the chains have been omitted,

FIG. 10 is a detail of the curved portion of the roller path between thehorizontal bottom portion at the tunnel entry and the commencement ofthe ascending portion of this tunnel showing, in addition, the chainconveyor and the articulation of the trays onto this conveyor.

As shown in the overall view, in FIGS. 1A and 1B (where the tunnel T isshown in section in order to assist understanding) the device accordingto the invention is constituted, generally speaking, of:

a. An endless chain conveyor 1, carrying trays 2 articulated at theirfront portion and equally spaced apart and moving continuously at auniform speed following a straight-line roller path CRcomprising, from afixed feed fork PC for the collections of articles P to a fixeddischarge fork FD for these articles, a horizontal portion 3 wherethe'operations of loading and of loosely wrapping these collections arecarried out, an ascending portion 4 having a slope close to the verticalin which the preheating and thermoshrinkage operation is carried out, ahorizontal portion 5 in which the thermoshrinkage finishing operation iscarried out, and a descending portion 6 in which the cooling operationis carried out and which leads into a horizontal portion 7 in the sameplane as the horizontal feed portion 3 and cooperating with thedischarge fork FD, and a return portion 8 in a plane below thesehorizontal portions;

b. A device 9 with heat sealing and cutting jaws, mounted along thehorizontal portion 3 so as to be capable of oscillating in the directionof movement (indicated by arrow F1) of the conveyor and in the reversedirection, in order to effect the sealing and cutting of the loosewrappings of film;

c. A device 10 (see FIGS. 4 to 7) for forming a loop 11 of slack in thelower film 12 between two consecutive collections of articles, situatedbehind the feed fork FC and serving also to place each collection ofarticles in a correct position upon the tray on which it rides;

d. A film reel handler 13, feeding the upper film 14 continuously andmounted above the device 9;

e. A similar reel handler 15, feeding the lower film 12 continuously andsituated behind and below the plane of the feed fork FC and to the sideof the axis of the conveyor;

f. A collectionforming conveyor 16, comprising at the front, close tothe fork PC, a feed loader 17 designed to push each of the collections Ponto this fork, before they are engaged by a tray 2, this feed loader 10being assisted by the device 10 in positioning this collection ofarticles upon this tray.

As can be seen in FIGS. 1A and 1B, the thermoshrinkage device proper isconstituted, generally speaking, of the roller path CR, substantially inthe form of an inverted, open U, followed by the conveyor 1 havingarticulated trays 2 for transporting the collections P, the right handarm of this U (in FIG. 1A) being sleeved in a hot air tunnel Tconstituting an ascending thermoshrinkage zone, the other arm situatedto the left (in FIG. 1B) and open to the surrounding air having above ita cooling assembly 32 which subjects it to cold air ventilation; thisconstitutes a descending cooling zone, at the exit S of which thecollections P are sufficiently rigid to be handled.

The roller path CR has its entry end E and exit end S connectedtogether, starting from the entry, by an ascending portion 4 having avery steep slope which nevertheless is less than the vertical, an upperhorizontal portion 5, and a descending portion 6, having a lesser slopethan that of the ascending portion.

The tunnel surrounding the entry end E, the ascending portion 4 and theupper portion 5 of the roller path. is of sufficient dimensions topermit the free passage through it, as seen in FIGS. 9 and 10, withinits heating assemblies 110, 111, of the conveyor chain 1, with its trays2 carrying the collections P of articles.

The cooling assembly 32 above the descending portion 6 and the exit endS of the roller path CR, open to the surrounding air, is constructed soas to feed cold air onto the collections P which have been subjected tothe shrinkage operation, after they leave the upper part 5 of thetunnel.

As can be seen in FIGS. 1A and 1B, and in FIGS. 2, 3 and 10, theconveyor 1 is constituted of two lateral chains guided on returnpinnions 18, 19, 20, 21, 22, 23 so as to follow a path substantiallyclose to that of the roller path CR. These chains support, transverselybetween them, the trays 2 by means of transverse shafts 116, arranged atequidistant spacing from one another and serving at each of their endsas a substitute for the articulation pin for the links of thecorresponding chain. Each shaft 116 supports in a freely pivoting mannerthe front portion of its corresponding tray 2, and also two lateralcrank assemblies situated at the sides and close to each of the chainsrespectively and between them. Each crank assembly comprises threecranks 117, 118, 119, rigidly connected together and having the form ofa three-branched fork. The free ends of the cranks 119 are connectedtogether by a rollerR passing transversely beneath the tray andsupporting it, while each of the cranks 117 and 118 carries,cantilevered at its end remote from the shaft 116, a guide roller Gintended for cooperating with the roller track defining path CR, eachroller being opposite to the other; that is to say, for example, theroller of crank 117 is on the chain side, while the roller of crank 118is on the side towards the median part of the tray, so that they maycooperate with lengths of roller tracks respectively 121, 122, offsetlaterally relative to one another depending upon the slope of the trackin such a way that the roller R, joining together the ends of the twocranks 119, always supports the tray 2 in a horizon tal position in theascending and/or descending portions of this roller path. Each tray 2comprises in addition, at its rear portion. two lateral rollers G1 forcooperating with the horizontal lengths 123 of the roller track in thehorizontal and descending portions of the roller path and while thecranks 117 and 118 are not working to support the tray in a horizontalposition, it being noted that when these cranks work the rollers G1 areunsupported.

As can be seen more particularly in the left hand portion of FIG. 1A andin the right hand portion of FIG. 1B, and also in FIGS. 8 and 9, theascending portion 4 in which the preheating and thermoshrinkageoperation is carried out, and also the horizontal portion of the rollerpath in which the thermoshrinkage finishing operation is carried out,are situated in the sleeveshaped tunnel T, following this roller path.This tunnel T constituting the ascending thermoshrinkage zone comprisesthree consecutive heating zones, a preheating zone Z1, correspondingsubstantially to the horizontal entry portion E and to the curvedcommencementof the ascending portion 4 of the roller path, a progressivethermoshrinkage zone Z2 corresponding to the ascending portion 4 and tothe curved commencement of the upper portion 5 of the roller path, and athermoshrinkage finishing zone Z3 corresponding tothis upper portion 5.

This tunnel supports, at its lower portion, an air ventilation assembly24, opening substantially into the preheating zone Z1, in its ascendingportion lateral groups 125 of heating resistors distributed on eitherside of the progressive thermoshrinkage zone Z2 and, in its upperportion, an air ventilation assembly 28 opening into the finishing zoneZ3, this zone comprising, at the sides, groups 127 of heating resistors.

The ventilation assembly 24 for the lower part is constituted of twoblowers V1 and V2, of the suction and delivery type, which areconstructed respectively on the one hand to supply air upwards onto thelateral groups 125 of resistance heaters contained in the ascendingducts 128 perforated by numerous blowing holes so as to direct jets ofhot air (indicated by the arrows) onto the collections of articles Pand, secondly, to re-extract the hot air collected by a recycling duct 129 situated beneath the ceiling of the tunnel (and perforated in thisregion) and redescending along the internal lateral walls of the tunnelto discharge at each of its bottom ends into the respective intake ofeach blower. The hot air is thus continuously recycled, thus tending toreduce the consumption of electricity by the resistance heaters.

' The ventilation assembly 28 for the upper part or finishing zone Z3,is also constituted of two blowers V3 and V4, of the suction anddelivery type, which are constructed respectively, on the one hand tofeed air upwards onto the lateral groups 127 of resistance heaterscontained in the ascending ducts 130 connected together across the topbeneath the ceiling of the tunnel by a duct portion 131, these ducts 130and 131 being perforated with numerous blowing holes to direct jets ofhot air (indicated by the arrows in FIG. 9) all around the collectionsof articles undergoing finishing thermoshrinkage and, secondly, tore-extract the hot air collected by a recycling duct 132, situatedbeneath the ceiling of the tunnel close to the exit from the tunnel (andperforated in this portion) and redescending along the lateral internalwalls of the tunnel to dis- 1 charge at each of its bottom ends into therespective inlet of each blower. As in the case of the progressivethermoshrinkage zone 22, the hot air is thus continuously recycled inthis finishing zone Z3.

It should be noted that in addition, in order to limit the hot airlosses, the tunnel T is provided, at its entry and at its exit, with alock 133 in the form of a slit curtain, to permit the passage of trayswith their collections of articles.

As can be seen more especially in FIG. 1B, the cooling assembly 32mounted above the descending portion is constituted of a number ofblowers (not shown) constructed to feed jets of cold air, indicated bythe arrows, onto the collections P in order that these collections shallbe well cooled, that is to a sufficiently low temperature for the shrunkplastics film to have readopted its initial properties and for it thusto be capable of being handled without risk of deforming, when it leavesthe exit S of the roller path.

It should be noted, in addition, that the roller track in thisdescending portion 6 below the cooling assembly is constructed tosupport only the rear rollers G] of the trays 2, a counter-rail 134being nevertheless provided to prevent these trays from tending to tipover forwards as they descend and thus not to retain their horizontalposition as far as the exit S.

As can be seen more especially in FIGS. 2 and 3, each tray 2 isconstituted by ribs 33 for supporting the collecting P of articles whichit bears, these ribs being arranged parallel to the axis of the conveyorand parallel to one another, and separated from one another by a gapwider than the width of each arm 34 of each of the forks FC and FD andslightly higher than the height of these, so that the upper planethrough the ribs is slightly above the plane of a fork when they arebrought by their tray 2 to the horizontal level at the feed anddischarge station, so that, at the feed fork FC (FIGS. 4 and 5) theyraise and entrain the lower film 12, upon which there rests a collectionof articles, and that at the discharge fork FD (FIG. 3), they lower anddeposit the collection of articles with its heat-shrunk wrapping uponthe fork. It should be noted that these ribs never pass upwardlycompletely through the gaps between the branches of the forks, eitherwhen ascending at FC or when descending at FD.

As shown in more detail but nevertheless a diagrammatic manner in FIGS.4 to 7, the sealing and cutting jaws device 9 is constituted of abalance arm 35 supportingan upper jaw36 and a lower jaw 37 reciprocatingwith their welding and cutting blades facing one another. These jaws areso arranged that, when the balance arm 35 is inclined in the directionopposite to the direction of motion of the conveyor, as indicated by thearrow F1 and seen in FIGS. 4 and 7, they grip between them the upperfilm 14 and lower film 12 between two successive collections ofarticles, heat seal them together and-cut their joint in two during theoscillation of the balance arm 35 in the direction of movement of I theconveyor, while the balance arm is in the position shown in FIG. 5, thatis to say sensibly in a position close to its vertical median position;at this stage, the balance arm continuing its oscillation in the samedirection, the jaws open and separate from one another until the lowerjaw 37 is at a lower position close to the axis of oscillation of thebalance arm and the upper jaw 36 is at an upper position above thecollections of articles, as shown in FIG. 6; at this stage, the balancearm 35 reversing its oscillation movement, that is to say moving in thedirection opposite to that of the conveyor motion, the upper jaw lowersthe upper film onto the collection to be wrapped, then the oscillationcontinuing and the collection'continuing to be entrained by its tray 2as shown in FIG. 7, this jaw presses the upper film 14 between thiscollection and the following one, while the lower jaw 37 bears on theunderside of the loop 11 of slack lower film 12, as shown in FIG. 4; at

this stage, the balance arm readopts its oscillation in the direction ofmotion of the conveyor and, also, of the collections of articles, andthe upper jaw 36 continues to descend and the lower jaw 37 to ascend,until they press the films against each other, while the balance arm isin the position shown in FIG. 5, the sequence of operations thencontinuing in the same order as previously described. It should be notedhowever that, during these operations, as the collections are taken overin succession by the trays 2, the loopforming device for forming thebulge or wave in the lower film 12 between two successive collections,comes into play at the same time as the loading device 17 in thesequence of steps represented in FIGS. 4 to 7, the lower film beingfirst raised as in FIG. 4 with its loop 11 jammed by its left sidebetween the rear edge of the collection on the tray which is aheadthereof and, at its right side, between the front edge of the followingcollection of articles and the rear of the feed fork FC, then with thedevice 10 dropping and drawing back, the loop 11 remains formed as shownin FIGS. 5 to 7, because the collections on the trays remain at the samespacing and are loaded at the same speed.

In addition, it should be noted that each of the reel handlers for theupper film and the lower film is of the type described in French patentNo. 2,198,476, filed on Sept. 1, 1972 in the name ofthe applicant, forapparatus for continuously feeding a strip from a reel to a machine; ageneral description of this apparatus is therefore all that will begiven here. Each of the reel handlers I3 and is constituted of a rollercradle designed to support a reel of film BU which is being used, and areserve reel of film BR, of heat sealing cutting jaws dcvicc M,comprising a central reversible jaw carrying the free end of the reservefilm and two fixed jaws. situated on either side of this reversible jaw,outside but close to the path ofthe film in use and the path which willbe that of the reserve film when it is in use, and of a film tensioningassembly for the film in use directing this film via a change directionroller device to the corresponding film feeder 38 for the upper film 14and 39 for the lower film 12. It will be noted however that theconstruction of eachreel handler is such that, when its film in usecomes to its end, its reversible jaw assisted by the corresponding fixedjaw joins the free end of the reserve film to this tail end of the usedfilm, the tensioning device releasing film during this operation, sothat there is no cessation of feed of film by the film feeder.

I claim:

1. A method for continuously packaging collections of articles in awrapping of thermoshrinkable plastics film, utilizing a conveyor movingcontinuously and carrying the unwrapped collections of articlesuninterruptedly one after another and delivering them, wrapped andclosed and ready to be handled, comprising the steps of:

depositing collections of articles in spaced succession upon a lowerfilm of heat scalable material at a feed 6 heat sealing the upper filmto the lower film between each adjacent pair of collections and cuttingeach heat sealed joint in half to provide a series of loosely wrappedcollections of articles;

transporting said series of loosely wrapped collections of articlessequentially through a preheating zone, then through a thermoshrinkagezone along an upwardly directed path, then through a thermoshrinkagefinishing zone and, finally, through a cooling zone along a downwardlydirected path to a discharge station where the collections, wrappedtightly and closed, may be immediately handled.

2. A method according to claim 1, including the steps of:

forming an upwardly arched loop of said lower film material rearwardlyof each collection of articles. at said feed staion, prior to deposit ofthe next succeeding collection on said film; and wherein said heatsealing step is performed by heat sealing said upper film to the crestof said loop.

3. A method according to claim 1 wherein said lower and upper films arecontinuously fed to said feed station, without cutting, and are of awidth exceeding the dimensions of the collections measured transverselyof said path so that they project beyond these collections laterally ofsaid path.

4. A method according to claim 2 wherein said arched loop of lower filmis formed rearwardly of one collection of articles and the succeedingcollection is placed and maintained on said lower film in postion tohold said loop.

5. A method according to claim 2 wherein the arched loop of said lowerfilm between two collections is formed so that its height is less thanthe height of each collection of articles so that, during theheat-sealing step the joint between said films is situated in a regionat the front and rear sides of each collection between the top andbottom thereof.

6. A device for packaging articles in a wrapping of thermoshrinkableplastics film, comprising:

a conveyor continuously movable along a path extending from a feedstaion to a discharge station, means between said stations for looselywrapping articles on said conveyor; means defining a preheating andthermoshrinkage station encompassing an upwardly directed portion ofsaid path; means defining a thermoshrinkage finishing station at ahorizontal portion of said path extending from the upper end of saidupwardly directed portion, and a station along a portion of said pathextending downwardly from said horizontal portion for cooling the shrunkwrappings;

an oscillating device at said feed station having means for heat sealingand cutting lower and upper films of material for forming a loosewrapping for each article;

means at said feed station for forming an upwardly arched loop of lowerfilm between two successive articles; and

a film reel handler feeding an upper film continuously to overlie saidarticles and a similar reel handler for feeding a lower film beneathsaid articles.

7. A device according to claim 6 wherein said conveyor is an endlesschain conveyor having equidistantly spaced pivotally mounted traysthereon on transverse axes, and means for holding said trayshorizontally ori' ented throughout the length of said path.

. further rollers so positioned as to run along horizontal portions ofsaid track means and to maintain each tray in the horizontal positionalong horizontal portions of said path.

9. A device according to claim 6, wherein said upwardly and downwardlydirected portions of said path and said recited horizontal portion aregenerally in the form of an inverted open U, one of the arms of this Ubeing sleeved by a hot air tunnel, constituting an ascendingthermoshrinkage zone, while the other arm is open to the surrounding airbut having above it a cooling assembly which subjects it to cold airventilation and constitutes a descending cooling zone, at the exit fromwhich the articles are sufficiently rigid to be capable of beinghandled.

10. A device according to claim 9 wherein:

said upwardly directed portion of each path is of very steep slope, andsaid downwardly directed portion is of a lesser slope.

11. A device according to claim 9 wherein said hot air tunnel, comprisesmeans defining three consecutive heating zones, the first or preheatingzone being at the entry portion thereof, the second or progressivethermoshrinkage zone proper extending along said upwardly directedportion of said path and commencement of the upperhorizontal portion ofsaid path, and the third or thermoshrinkage finishing zone extendingalong said upper portion.

12. A device according to claim 9 wherein said tunnel includes. at itslower part, an air ventilation assem bly opening into the commencementof the ascending portion close to the preheating zone; saidthermoshrinkage zones including lateral-groups of resistance heatersdistributed therein and, in its upper portion, an air ventilationassembly opening into the finishing zone and, within this finishingzone, lateral groups of resistance heaters. I

13. A device according to claim 12 wherein said firstnamed ventilationassembly comprises at least one blower, of the suction and'deliverytype, arranged to feed air upwards onto the groups of resistance heatersto provide progressively hotter air to the collections as they ascendand to re-extract this hot air at the ceiling of the ascending portion,by means of a recycling duct extending beneath the ceiling anddescending to the blower along the internal walls of the ascendingportion, the portion of this duct beneath the ceiling being providedwith numerous intake holes.

'14. A device according to claim 12 wherein the lastnamed ventilationassembly comprises at least one blower, of the suction and deliverytype, arranged to feed air upwards onto the groups of resistance heatersto provide hot air to the collections advancing through the finishingzone towards the exit from the tunnel, and to re-extract this hot air atthe ceiling of this zone, by means of a recycling duct extending beneaththe ceiling of the upper part of the tunnel and descending to the bloweralong the internal walls of the upper portion, the portion of this ductbeneath the ceiling being provided with numerous intake holes.

15. A device according to claim 14 wherein the resistance heaters are inthe form of finned resistance heaters and are arranged in tiers allalong the internal lateral walls of the tunnel, both in its ascendingportion and in its upper portion and are placed in front of thedescending hot air recycling ducts, towards the median plane of thetunnel, in order to ensure good heat distribution.

16. A device according to claim 15 wherein each ventilation assembly isarranged to deliver air into ducts having resistance heaters therein;said ducts, in the ascending portion of the tunnel, being situated infront of the recycling ducts towards themedian plane of the tunnel andbeing perforated, in the side towards this plane, to constitute a hotair blowing chamber having perforated lateral and lower walls, theceiling of which is traversed by the perforated portion of the recyclingduct and, in the upper part of the tunnel, being situated in the samemanner but to constitute a hot air blowing chamber completelysurrounding the finishing zone and having perforated lateral, upper andlower walls, the perforated portion of the recycling duct being situatedbeneath the ceiling of this upper part of the tunnel, in front of thechamber and close to the exit from the tunnel, this tunnel being, inaddition, provided with a lock at its entry and at its exit. in the formof hanging, slotted curtains, to permit the passage of the trays andtheir collections of articles, in order to limit the hot air losses.

17. A device according to claim 16 wherein the descending portion ofsaid path, in'which cooling is' carried out, is situated so as to beexposed to the surround ing air and having thereabove a cooling assemblyconstituted of a ventilation assembly arranged to direct jets of coldair onto each of-the collections having shrunk wrappings to acceleratetheir cooling.

.18. A device according to claim-l7 wherein each tray of the conveyor isconstituted of ribs for supporting the article resting upon it, saidribs extending parallel to the direction of travel of the conveyorandparallel to one another, separated from one another by a gap exceedingthe width of each arm of each of fixed forks and slightly higher thanthe height of said arms, whereby the upper plane of said ribs areslightly above that of a fork when they are brought by their respectivetray to the horizontal at the feed and discharging stations, so that atthe feed fork they raise and entrain the lower film with an articleresting upon it and that at the discharge fork they lower and depositthe article with its shrunk wrapping upon the fork, without evercompletely passing through the arms of these forks.

19. A device according to claim l8wherein said 05- cillating devicecomprises a balance arm supporting an upper jaw and a lower jawreciprocating with their respective heat sealing and cutting bladesopposite each other, means for actuating said jaws so that, when theirbalance arm is inclined in the direction opposite to the direction ofmotion of the conveyor, they grip between them the upper and lower filmsbetween two successive articles, heat seal them and cut their jointduring the oscillation of the balance arm in the direction of mo-- tionof the conveyor, when it is substantially in a position close to itsmedian vertical position, they open and move apart from each other whenthe balance arm continues its oscillation in the same direction untilthe lower jaw is at a lower position close to the axis of oscillation ofthe balance arm and the upper jaw is at a position above thecollections, this upper jaw then lowering the upper film onto thecollection of articles to be wrapped while the balance arm makes itsreverse oscillation to return to its initial position, at which instantthe lower jaw bears up against the underside of the loop of lower filmand the upper jaw bears down on the upper film so as to place it ontothe top of this loop, gripping the films, and repeating the describedcycle of operations.

20. A device according to claim 19 wherein each film reel handler isconstituted ofa roller cradle arranged to support a reel of film in useand a reserve reel, ofa heat sealing and cutting device comprising acentral reversible jaw, carrying the free end of the reserve film andtwo fixed jaws, situated on either side of this reversible jaw outsidebut adjacent the path of the film in use and to the path which will bethat of the reserve film when it is being used, and of a film tensioningdevice for the film in use, means for directing this film via adirection changing assembly towards the corresponding film feeder of thepackaging device, the construction of this reel handler being such that,when the film in use comes to an end, the reversible jaw, assisted bythe corresponding fixed jaw, joins the free end of the reserve film tothe tail end of the used film, the tensioning device liberating filmduring this operation so that there is no cessation of feed of film bythe film feeder.

1. A method for continuously packaging collections of articles in awrapping of thermoshrinkable plastics film, utilizing a conveyor movingcontinuously and carrying the unwrapped collections of articlesuninterruptedly one after another and delivering them, wrapped andclosed and ready to be handled, comprising the steps of: depositingcollections of articles in spaced succession upon a lower film of heatsealable material at a feed station; covering of the collections with anupper film of said material; heat sealing the upper film to the lowerfilm between each adjacent pair of collections and cutting each heatsealed joint in half to provide a series of loosely wrapped collectionsof articles; transporting said series of loosely wrapped collections ofarticles sequentially through a preheating zone, then through athermoshrinkage zone along an upwardly directed path, then through athermoshrinkage finishing zone and, finally, through a cooling zonealong a downwardly directed path to a discharge station where thecollections, wrapped tightly and closed, may be immediately handled. 1.A method for continuously packaging collections of articles in awrapping of thermoshrinkable plastics film, utilizing a conveyor movingcontinuously and carrying the unwrapped collections of articlesuninterruptedly one after another and delivering them, wrapped andclosed and ready to be handled, comprising the steps of: depositingcollections of articles in spaced succession upon a lower film of heatsealable material at a feed station; covering of the collections with anupper film of said material; heat sealing the upper film to the lowerfilm between each adjacent pair of collections and cutting each heatsealed joint in half to provide a series of loosely wrapped collectionsof articles; transporting said series of loosely wrapped collections ofarticles sequentially through a preheating zone, then through athermoshrinkage zone along an upwardly directed path, then through athermoshrinkage finishing zone and, finally, through a cooling zonealong a downwardly directed path to a discharge station where thecollections, wrapped tightly and closed, may be immediately handled. 2.A method according to claim 1, including the steps of: forming anupwardly arched loop of said lower film material rearwardly of eachcollection of articles, at said feed staion, prior to deposit of thenext succeeding collection on said film; and wherein said heat sealingstep is performed by heat sealing said upper film to the crest of saidloop.
 3. A method according to claim 1 wherein said lower and upperfilms are continuously fed to said feed station, without cutting, andare of a width exceeding the dimensions of the collections measuredtransversely of said path so that they project beyond these collectionslaterally of said path.
 4. A method according to claim 2 wherein saidarched loop of lower film is formed rearwardly of one collection ofarticles and the succeeding collection is placed and maintained on saidlower film in position to hold said loop.
 5. A method according to claim2 wherein the arched loop of said lower film between two collections isformed so that its height is less than the height of each collection ofarticles so that, during the heat-sealing step the joint between saidfilms is situated in a region at the front and rear sides of eachcollection between the top and bottom thereof.
 6. A device for packagingarticles in a wrapping of thermoshrinkable plastics film, comprising: aconveyor continuously movable along a path extending from a feed staionto a discharge station, means between said stations for loosely wrappingarticles on said conveyor; means defining a preheating andthermoshrinkage station encompassing an upwardly directed portion ofsaid path; means defining a thermoshrinkage finishing station at ahorizontal portion of said path extending from the upper end of saidupwardly directed portion, and a station along a portion of said pathextending downwardly from said horizontal portion for cooling the shrunkwrappings; an oscillating device at said feed station having means forheat sealing and cutting lower and upper films of material for forming aloose wrapping for each article; means at said feed station for formingan upwardly arched loop of lower film between two successive articles;and a film reel handler feeding an upper film continuously to overliesaid articles and a similar reel handler for feeding a lower filmbeneath said articles.
 7. A device according to claim 6 wherein saidconveyor is an endless chain conveyor having equidistantly spacedpivotally mounted trays thereon on transverse axes, and means forholding said trays horizontally oriented throughout the length of saidpath.
 8. A device according to claim 7, wherein said last-named meanscomprise crank arms fixed to said trays and having guide rollers fixedto their free ends, and track means adjacent said path and so configuredto engage said rollers and maintain the trays in a horizontal positionat all times in the upwardly directed and downwardly directed portionsof said path, each tray having further rollers so positioned as to runalong horizontal portions of said track means and to maintain each trayin the horizontal position along horizontal portions of said path.
 9. Adevice according to claim 6, wherein said upwardly and downwardlydirected portions of said path and said recited horizontal portion aregenerally in the form of an inverted open U, one of the arms of this Ubeing sleeved by a hot air tunnel, constituting an ascendingthermoshrinkage zone, while the other arm is open to the surrounding airbut having above it a cooling assembly which subjects it to cold airventilation and constitutes a descending cooling zone, at the exit fromwhich the articles are sufficiently rigid to be capable of beinghandled.
 10. A device according to claim 9 wherein: said upwardlydirected portion of each path is of very steep slope, and saiDdownwardly directed portion is of a lesser slope.
 11. A device accordingto claim 9 wherein said hot air tunnel, comprises means defining threeconsecutive heating zones, the first or preheating zone being at theentry portion thereof, the second or progressive thermoshrinkage zoneproper extending along said upwardly directed portion of said path andcommencement of the upper horizontal portion of said path, and the thirdor thermoshrinkage finishing zone extending along said upper portion.12. A device according to claim 9 wherein said tunnel includes, at itslower part, an air ventilation assembly opening into the commencement ofthe ascending portion close to the preheating zone; said thermoshrinkagezones including lateral groups of resistance heaters distributed thereinand, in its upper portion, an air ventilation assembly opening into thefinishing zone and, within this finishing zone, lateral groups ofresistance heaters.
 13. A device according to claim 12 wherein saidfirst-named ventilation assembly comprises at least one blower, of thesuction and delivery type, arranged to feed air upwards onto the groupsof resistance heaters to provide progressively hotter air to thecollections as they ascend and to re-extract this hot air at the ceilingof the ascending portion, by means of a recycling duct extending beneaththe ceiling and descending to the blower along the internal walls of theascending portion, the portion of this duct beneath the ceiling beingprovided with numerous intake holes.
 14. A device according to claim 12wherein the last-named ventilation assembly comprises at least oneblower, of the suction and delivery type, arranged to feed air upwardsonto the groups of resistance heaters to provide hot air to thecollections advancing through the finishing zone towards the exit fromthe tunnel, and to re-extract this hot air at the ceiling of this zone,by means of a recycling duct extending beneath the ceiling of the upperpart of the tunnel and descending to the blower along the internal wallsof the upper portion, the portion of this duct beneath the ceiling beingprovided with numerous intake holes.
 15. A device according to claim 14wherein the resistance heaters are in the form of finned resistanceheaters and are arranged in tiers all along the internal lateral wallsof the tunnel, both in its ascending portion and in its upper portionand are placed in front of the descending hot air recycling ducts,towards the median plane of the tunnel, in order to ensure good heatdistribution.
 16. A device according to claim 15 wherein eachventilation assembly is arranged to deliver air into ducts havingresistance heaters therein; said ducts, in the ascending portion of thetunnel, being situated in front of the recycling ducts towards themedian plane of the tunnel and being perforated, in the side towardsthis plane, to constitute a hot air blowing chamber having perforatedlateral and lower walls, the ceiling of which is traversed by theperforated portion of the recycling duct and, in the upper part of thetunnel, being situated in the same manner but to constitute a hot airblowing chamber completely surrounding the finishing zone and havingperforated lateral, upper and lower walls, the perforated portion of therecycling duct being situated beneath the ceiling of this upper part ofthe tunnel, in front of the chamber and close to the exit from thetunnel, this tunnel being, in addition, provided with a lock at itsentry and at its exit, in the form of hanging, slotted curtains, topermit the passage of the trays and their collections of articles, inorder to limit the hot air losses.
 17. A device according to claim 16wherein the descending portion of said path, in which cooling is carriedout, is situated so as to be exposed to the surrounding air and havingthereabove a cooling assembly constituted of a ventilation assemblyarranged to direct jets of cold air onto each of the collections havingshrunk wrappings to accelerate their cooling.
 18. A device according toclaim 17 wherein each tray of the conveyor is constituted of ribs forsupporting the article resting upon it, said ribs extending parallel tothe direction of travel of the conveyor and parallel to one another,separated from one another by a gap exceeding the width of each arm ofeach of fixed forks and slightly higher than the height of said arms,whereby the upper plane of said ribs are slightly above that of a forkwhen they are brought by their respective tray to the horizontal at thefeed and discharging stations, so that at the feed fork they raise andentrain the lower film with an article resting upon it and that at thedischarge fork they lower and deposit the article with its shrunkwrapping upon the fork, without ever completely passing through the armsof these forks.
 19. A device according to claim 18 wherein saidoscillating device comprises a balance arm supporting an upper jaw and alower jaw reciprocating with their respective heat sealing and cuttingblades opposite each other, means for actuating said jaws so that, whentheir balance arm is inclined in the direction opposite to the directionof motion of the conveyor, they grip between them the upper and lowerfilms between two successive articles, heat seal them and cut theirjoint during the oscillation of the balance arm in the direction ofmotion of the conveyor, when it is substantially in a position close toits median vertical position, they open and move apart from each otherwhen the balance arm continues its oscillation in the same directionuntil the lower jaw is at a lower position close to the axis ofoscillation of the balance arm and the upper jaw is at a position abovethe collections, this upper jaw then lowering the upper film onto thecollection of articles to be wrapped while the balance arm makes itsreverse oscillation to return to its initial position, at which instantthe lower jaw bears up against the underside of the loop of lower filmand the upper jaw bears down on the upper film so as to place it ontothe top of this loop, gripping the films, and repeating the describedcycle of operations.